1. Field of the Invention
The present invention relates to robotic manipulators, and in particular to cost-effective sensing systems for robotic manipulator. More particularly, this invention relates to inertial sensing applied to robotic manipulators.
2. Description of the Related Art
Currently, robots and remote manipulators with superior and reliable closed loop control are expensive because they employ multiple joints with expensive joint servo controllers. The high cost of motion sensors is a principal reason for the expense and weight of the joint servos of robotic manipulators and as a consequence the utility of robots versus other means of delivery or production, e.g. human labor. Typically, six joints are utilized with a tachometer and a position encoder employed at each joint, often at the input of a heavy, mechanically stiff, high class gear reduction system to increase output torque capability while maintaining output position accuracy. This is the design today of the Shuttle Remote Manipulator System (SRMS) which is 50 ft long comprising two shoulder joints, an elbow joint and three wrist joints and an end effector for payload grappling.
In addition, the sensors employed for robotic manipulators are often electromagnetic inductosyns, resolvers or optical position encoders. All such devices are inherently expensive if mounted at the joint output because they require large circumferential sensing discs around each joint. For example, the SRMS output joint diameters are of the order of eight inches. The overall joint position is monitored for low frequency joint position control but for robust dynamic rate control during maneuvers, under resolved rate joint control, the bandwidth and rate resolution of such a sensor becomes challenging. For resolved rate joint control, a separate relative rate motion sensor, e.g. inductosyn tachometer is mounted to the higher speed reduction gearbox input shaft. However, for accurate performance in this mode, the output precision and stiffness requirements for the gearing are high, e.g. class 13, and hence the cost and weight are also very high. These cost, weight, power and performance of these sensors is inadequate for applications capable of matching human operational performance in robust, reliable, smooth closed loop joint operation. For example, the resolution and bandwidth of such sensors would require heavy and expensive gearing, making such performance prohibitive for most applications. Furthermore, robot or manipulator end effector navigation, guidance and control that is based on electromagnetic sensors or optical vision sensors alone, is not capable of matching human performance and reliability, even when employing a state of the art digital computer.
Thus, there is a need for a simple, lightweight and inexpensive joint and end effector sensor and system solution for use in robotic manipulators. There is further a need for such a sensor system to provide robust, reliable and highly accurate sensing for lightweight joints to enable human operation performance levels. The present invention satisfies all these needs.